Soakaway and patio advice

[3xAAA]

I’m planning to build an 18m² patio at the far end of my garden for a hot tub and some loungers. The problem is I’ve got no existing drainage to tie into, so I think a soakaway is my only realistic option.

I’ve read very mixed views on soakaways - some people say they work perfectly fine, others say they’re a waste of time. In this case it would only be dealing with surface water from rain and the occasional jet wash, not draining the hot tub itself. If they do work well in practice, I’d really appreciate any guidance on sizing for a patio this size.

I’m also a bit stuck on the fall required. I know hot tubs should ideally sit on a perfectly level base, but I still need to manage drainage. Would you keep the whole patio dead level and use ACO drains around the edges feeding into the soakaway? Or is it better to build in a slight fall after the hot tub, towards the garden/grass side and collect water with a channel drain before a sleeper border?

Lastly, there’s a corner of what will become the lawn (marked in red on the photo) that stays boggy and soft even days after rain. I’ve already stripped the old ground and laid around 200mm of loamy soil over a rotovated base, but it still holds water. Not sure what I’m missing here, so any ideas would be appreciated.

Happy to be told if I’m overcomplicating things or missing something obvious.

[sherman]

Hide the soakaway under the hot tub?

For the boggy corner I would put a gravel grid or 2 just under the grass level and grow the grass through it. Then you can walk on it and the grid will disipate your weight over the boggy ground.

[3xAAA]

I could build it under the patio, but I'd be a bit wary of having such a large amount of weight resting on top of it. Seems more sensible to build it under the lawn - at least then I could always reknew it/enlarge it at a later date if needed.

[ATG]

The soak away's performance will be determined by the type of soil you're on. If there's a solid pan of clay a couple of foot down, it won't work at all. If you've got sandy soil on top of limestone or chalk, the water will disappear so quickly you hardly need to engineer anything.

[3xAAA]

There is clay in spots, but not everywhere.

I suppose I could dig a 1m x 1m x 1m hole and see what that turns up - I'm guessing that would suffice for 18 square metres.